Method for the purification of an alpha-hydroxy acid on an industrial scale

Abstract

The invention relates to a method for the purification of a fermentatively prepared α-hydroxy acid on an industrial scale, in which an α-hydroxy acid with a color (fresh) of not more than 10,000 APHA units is subjected to at least two crystallization steps, with the crystallization steps being carried out in cooling crystallization devices, melting crystallization devices, evaporative crystallization devices and/or adiabatic crystallization devices.

1. Method for the purification of a fermentatively prepared α-hydroxy acid on an industrial scale, in which an α-hydroxy acid with a colour (fresh) of not more than 10,000 APHA units is subjected to at least two crystallization steps, with the crystallization steps being carried out with water as a solvent or without any solvent in cooling crystallization devices, melting crystallization devices, evaporative crystallization devices and/or adiabatic crystallization devices. 
     
     
       2. Method according to  claim 1 , in which the α-hydroxy acid is lactic acid or glycolic acid. 
     
     
       3. Method according to  claim 2 , in which the α-hydroxy acid is lactic acid. 
     
     
       4. Method according to  claim 1 , in which two crystallization steps are applied. 
     
     
       5. Method according to  claim 4 , in which the crystallization steps are carried out in one device. 
     
     
       6. Method according to  claim 1 , in which the product stream from the crystallization steps is separated into a mother liquor and α-hydroxy acid crystals by means of solid-liquid separation. 
     
     
       7. Method according to  claim 1 , in which, if applicable, the chiral purity of the α-hydroxy acid is at least 90% with a colour (fresh) of not more than 10,000 APHA units. 
     
     
       8. Method according to  claim 1 , in which the α-hydroxy acid is prepared fermentatively, with a colour (fresh) of not more than 3000 APHA units. 
     
     
       9. Method according to  claim 1 , in which the cooling crystallization is carried out by direct cooling of a condensed, liquid concentrate or distillate of the α-hydroxy acid. 
     
     
       10. Method according to  claim 1 , in which the melting crystallization is carried out by direct cooling of a condensed, liquid concentrate or distillate which contains the α-hydroxy acid in a molten state. 
     
     
       11. Method according to  claim 1 , in which the evaporative crystallization is carried out by (1) diluting a condensed, liquid concentrate or distillate of the α-hydroxy acid with water and (2) evaporation of water. 
     
     
       12. Method according to  claim 1 , in which the adiabatic crystallization is carried out by evaporation of water without supplying heat.